1. Field of the Invention
The present invention is in general related to an integrated circuit. More specifically, the present invention is related to a four-quadrant multiplier, which employs BiCMOS (Bipolar-Complementary MOS) devices and can be utilized in applications of high-frequency operation.
2. Description of the Prior Art
Multipliers are very essential components serving as building blocks for a large number of applications, such as adaptive filters, frequency doublers, and modulators. The operation of a four-quadrant multiplier, which is a kind of multiplier, involves receiving a first input signal V.sub.1, a second input signal V.sub.2, a third input signal V.sub.3, and a fourth input signal, yielding a product signal V.sub.4, which is the result of multiplication operation of the voltage differences V.sub.1 -V.sub.2 and V.sub.3 -V.sub.4.
In bipolar transistor technology, Gilbert cells are usually used to build a four-quadrant multiplier. But in MOS transistor technology, four approaches have emerged. The first approach, similar to the case of bipolar technology, is to use Gilbert cells to build a four-quadrant multiplier. The second approach is to use the properties of MOS transistors operated in the saturation region to design multipliers. The saturation region is also called an active region, where the drain current value is proportional to the square of the gate-drain voltage value. The third approach is to use the properties of MOS transistors operated in the linear region to design multipliers. The linear region is also called a triode region, where the drain current value is linearly proportional to the gate-source voltage when the drain-source voltage is a constant. The fourth or last approach uses the properties of MOS transistors operated in the subthreshold region to design multipliers.
On the other hand, the emergence of BiCMOS ICs comprising bipolar and MOS transistors offers a new opportunity to improve the performance of integrated circuits. BiCMOS makes it possible to implement circuits with high densities, like CMOS, which consume less power than bipolar ICs, but which offer speeds faster than those possible with CMOS alone.